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 A212629 Number of vertices in all maximal independent vertex subsets in the rooted tree with Matula-Goebel number n. 11
 1, 2, 3, 3, 6, 6, 4, 4, 9, 9, 9, 8, 8, 8, 14, 5, 8, 15, 5, 11, 11, 14, 15, 10, 22, 15, 25, 10, 11, 20, 14, 6, 22, 11, 17, 19, 10, 10, 20, 13, 15, 18, 10, 17, 33, 25, 20, 12, 13, 28, 17, 18, 6, 36, 32, 12, 13, 20, 11, 24, 19, 22, 29, 7, 31, 31, 10, 13, 33, 24, 13, 23, 18, 19, 45, 12, 26, 32 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS A vertex subset in a tree is said to be independent if no pair of vertices is connected by an edge. The empty set is considered to be independent. An independent vertex subset S of a tree is said to be maximal if every vertex that is not in S is joined by an edge to at least one vertex of S. The Matula-Goebel number of a rooted tree can be defined in the following recursive manner: to the one-vertex tree there corresponds the number 1; to a tree T with root degree 1 there corresponds the t-th prime number, where t is the Matula-Goebel number of the tree obtained from T by deleting the edge emanating from the root; to a tree T with root degree m>=2 there corresponds the product of the Matula-Goebel numbers of the m branches of T. Let A(n)=A(n,x), B(n)=B(n,x), C(n)=C(n,x) be the generating polynomial with respect to size of the maximal independent sets that contain the root, the maximal independent sets that do not contain the root, and the independent sets which are not maximal but become maximal if the root is removed, respectively. We have: A(1)=x, B(1)=0, C(1)=1, A(t-th prime) = x[B(t) + C(t)], B(t-th prime) = A(t), C(t-th prime)=B(t), A(rs)=A(r)A(s)/x, B(rs)=B(r)B(s)+B(r)C(s)+B(s)C(r), C(rs)=C(r)C(s) (r,s>=2). The generating polynomial of the maximal independent vertex subsets with respect to size is P(n, x)=A(n,x)+B(n,x). Then a(n)=subs(x=1, dP(n,x)/dx). The Maple program is based on these relations. LINKS É. Czabarka, L. Székely, and S. Wagner, The inverse problem for certain tree parameters, Discrete Appl. Math., 157, 2009, 3314-3319. E. Deutsch, Rooted tree statistics from Matula numbers, arXiv:1111.4288 [math.CO], 2011. F. Goebel, On a 1-1-correspondence between rooted trees and natural numbers, J. Combin. Theory, B 29 (1980), 141-143. I. Gutman and A. Ivic, On Matula numbers, Discrete Math., 150, 1996, 131-142. I. Gutman and Yeong-Nan Yeh, Deducing properties of trees from their Matula numbers, Publ. Inst. Math., 53 (67), 1993, 17-22. D. W. Matula, A natural rooted tree enumeration by prime factorization, SIAM Rev. 10 (1968) 273. H. S. Wilf, The number of maximal independent sets in a tree, SIAM J. Alg. Disc. Math., 7, 1986, 125-130. FORMULA a(n) = Sum(k*A212627(n,k), k>=1). EXAMPLE a(11)=9 because the rooted tree with Matula-Goebel number 11 is the path tree on 5 vertices R - A - B - C - D; the maximal independent vertex subsets are {R,C}, {A,C}, {A,D}, and {R,B,D}. MAPLE with(numtheory): P := proc (n) local r, s, A, B, C: r := n-> op(1, factorset(n)): s := n-> n/r(n): A := proc (n) if n = 1 then x elif bigomega(n) = 1 then x*(B(pi(n))+C(pi(n))) else A(r(n))*A(s(n))/x end if end proc: B := proc (n) if n = 1 then 0 elif bigomega(n) = 1 then A(pi(n)) else sort(expand(B(r(n))*B(s(n))+B(r(n))*C(s(n))+B(s(n))*C(r(n)))) end if end proc: C := proc (n) if n = 1 then 1 elif bigomega(n) = 1 then B(pi(n)) else expand(C(r(n))*C(s(n))) end if end proc: if n = 1 then x else sort(expand(A(n)+B(n))) end if end proc: seq(subs(x = 1, diff(P(n), x)), n = 1 .. 120); CROSSREFS Cf. A206499, A212627, A212618-A212632. Sequence in context: A347732 A075258 A321745 * A127779 A207634 A222862 Adjacent sequences: A212626 A212627 A212628 * A212630 A212631 A212632 KEYWORD nonn AUTHOR Emeric Deutsch, Jun 08 2012 EXTENSIONS Sequences A212618-A212632 edited by M. Marcus and M. F. Hasler, Jan 06 2013 STATUS approved

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Last modified February 7 12:58 EST 2023. Contains 360123 sequences. (Running on oeis4.)